U.S. Pat. No. 4,674,834 issued June 23, 1987 and now assigned to the assignee of the present application discloses a page scanner using a noncoherent bundle of optical fibers extending from a linear entrance face to an area exit face. The pixels in the area face are imaged onto an array of photosensors. The fiber ends in the area face are random with respect to the positions of the fiber ends in the linear face. Accordingly, the bundle is "noncoherent" and the pixels exiting the area face are scrambled.
An initialization procedure provides an implementation to unscramble the pixels electronically. The procedure is operative to move a light slit, narrower than a fiber end, along the linear face of the bundle and interrogating the sensor array to determine the addresses of sensors illuminated for each position of the slit. A computer program is operative to select a single address in each instance and to place those addresses in a sequence which corresponds to the sequence of slit positions. Thus, the pixel data outputs from the sensor array are organized to correspond to the ordered sequence of pixels in the entrance face.
Later, in normal use of the scanner, the linear end is positioned astride a document, a scan line or segment of the document is illuminated, and the address sequence or string, conveniently stored in ROM, is triggered to interrogate the selected sequence of sensor addresses (corresponding to the sequence of pixels in the linear face), to determine the light level associated with each pixel.
The page is then moved, with respect to the linear face, and the process is repeated. In this manner, a page is scanned and the pixel data in the sensor array related to the consecutive scan lines are properly organized even though a noncoherent fiber bundle is used.
U.S. Pat. No. 4,748,680 issued May 31, 1988 and also now assigned to the assignee of the present application discloses a color scanner. The color scanner employs three fiber optic bundles and, in one embodiment, employs dichroic transmission filters (red, green, and blue) on the area faces of the three bundles. The area faces are imaged onto different regions of a single large sensor array associated with different color descriptors or they are imaged onto three different sensor arrays. This technique is relatively expensive because it requires three fiber bundles and three sensor arrays or a single large sensor array.
An alternative technique requires time sequential color illumination with a monochrome sensor array. But this technique requires three times as long for scanning a line, and three light sources, or a white light source and a color wheel.
The problem to which the present invention is directed is to produce a color scanner which utilizes a monochrome sensor array without the expense of three fiber optic bundles or the time consuming time sequential operation and three illumination sources. The invention is based on the recognition that so long as each fiber end in the area face of the fiber optic bundle corresponds to a plurality of sensors of the photosensor array, three sensors can be selected to correspond to each fiber end and those sensors can be color coded as well as placed in the proper sequence as noted above.
The color coding is introduced by placing a filter with a repetitive pattern of vertical red, green, and blue (or yellow, cyan and magenta) stripes of such dimensions that at least four stripes correspond to the image of the fiber end on the sensor the filter. A second lens is used to focus the image from the filter (now color coded) onto the photosensor array.